Division of Radiooncology, Deutsches Krebsforschungszentrum, 69120 Heidelberg, Germany
We have to recognize that antigen alteration can be poorly controlled in the course of tissue preparation. In many cases, attempts of antigen retrieval must be tried in order to “unmask” epitopes. The localization of antigens can be significantly improved by pretreatment of tissue sections with so-called antigen-retrieval reagents and by physical means such as heat, e.g. microwave oven, pressure cooker or steamer. Two major procedures for antigen retrieval are common for formaldehyde fixed and paraffin embedded tissue specimens: heat-induced epitope retrieval (HIER) and proteolytic-induced epitope retrieval (PIER). Moreover, pretreatment of tissue sections with defined blocking solutions are necessary to reduce background reactions.